This application claims priority under 35 U.S.C. xc2xa7xc2xa7 119 and/or 365 to Application Ser. No. 199 56 152.4 filed in Germany on Nov. 23, 1999; the entire content of which is hereby incorporated by reference.
The invention refers to a method for manufacturing a multi-layer material, particularly as a preformed part for the inside roof lining of an automobile, where a plastic foam material is equipped with a fiber reinforcement and at least one top layer. Furthermore, the invention refers to a multi-layer material, particularly as a preformed part for the inside roof lining of an automobile, which contains a plastic foam layer with a top layer on at least one side and a fiber reinforcement.
A preferred application area for the invention is the manufacturing of a preformed part for the inside roof lining of an automobile. The invention will be illustrated accordingly in this context. It is, however, also applicable in other cases, for example for the interior molding of vehicles or for the interior lining of containers.
With the development of the self-supporting one-piece interior automobile roof lining, which is supplied to the vehicle manufacturer as a preformed and installable part, began the change from the purely decorative covering to a xe2x80x9cmultifunctionalxe2x80x9d unit that, for example, can also be used for optical display elements or as covering and seating element for a head airbag. The inside automobile roof lining is often manufactured from a multi-layer material that initially is just a sheet material and is then formed into the xe2x80x9ccorrectxe2x80x9d shape through the application of pressure and heat.
EP 0 248 199 B1 displays a multi-layer lining element with a core of polyurethane rigid foam as the base layer. Both sides of this base layer are equipped with a coat of an acrylonitrile-butadiene-styrene foil. The polyurethane base layer has been bonded to the coat with a foaming process. On the visible side, a decorative coat is glued on with the help of a bonding sheet. With this lining element, the glass fibers used up to now are replaced by thermoplastics.
DE 35 16 132 C2 describes a multi-layer, molded interior lining for passenger cars, particularly an inside roof lining, where glass fiber mats are applied to the interior foam layer on both sides. When such a material is subject to deformation, the risk that the glass fibers stretch excessively and that voids are created arises.
DE 35 21 828 C2 describes a method for manufacturing preformed polyurethane foam parts reinforced with fibrous web mats, which can be used for example as interior lining in vehicles.
For this, several glass fiber mats are inserted into a form tool, while adding an intermediate sisal fiber mat layer, and a reaction mixture, which fills in the cavity within the fibrous web mats and forms a polyurethane foam, is placed in the cavity of the form tool.
The task of the invention is to simplify the manufacturing process of a multi-layer material.
This task is resolved with the method mentioned previously in which a fibrous web is combined with a free-flowing mixture of foaming components and is then run through a belt press.
With this design, a continuous process can be realized. The foaming components can penetrate the fibrous web as long as they are still in the free-flowing state. During the subsequent building of the foam, the fibrous web is located in the middle of the foam. The expansion of the foam is defined through the belt press. Placement of the fibers in the middle of the foam prevents dangerous and rigid fiber bundles and edges, which can e.g. lead to significant injuries after the material breaks due to the release of a head air bag. In addition, the risk of damage in subsequent forming and pressing processes is significantly reduced. The fibers are mainly located in the center of the foam layer and are therefore protected by the foam layer.
Basically all foaming materials can be used for the foam, particularly polyurethane in which the free-flowing mixture is made up of polyhydric alcohol and isocyanate and corresponding catalysts. However, polyester is also a possible foaming material. The fibrous web is preferably a glass fiber web. Polyester fibrous webs are possible as well.
Preferably, the top layer is tight against to the mixture and the foam that will develop from it, and the top layer is run through the belt press together with the saturated fibrous web. This design prevents soiling of the belt press from the foam. At the same time, the top layer is firmly glued together with the foam. This way, a very homogeneous material is obtained with good usage properties. Usually both sides of the foam are equipped with the top layer. The top layers then form the outer surfaces of the foam layer.
Preferably, a bonding sheet is selected as the top layer and another sheet material is run through the belt press along with it on the outer side. The bonding sheet itself can be adhesive already. It is also possible for it to become adhesive only due to the reaction temperature occurring during the foaming process. For example a modified PE-foil can be used, which softens with the reaction temperature and then serves as an adhesive for the other sheet material. After running through the belt press, i.e. virtually with a single process, the multi-layer material is available.
In a preferred version, a counteracting material is applied to one side as a sheet material, and a decorative material is applied to the opposite side. The multi-layer material is then already complete for further processing into an inside roof lining for an automobile or into another interior covering part.
The foaming components are preferably added shortly before the belt press so that the majority of the foaming process occurs within the belt press. This presents several advantages. For one, the dimensional exactness of the multi-layer material can be controlled better because the belt press limits the expansion of the foam during the foam reaction. The second advantage is that a lower amount of feeding force is required because the foamed material must no longer be pressed together. Finally the consistency or the inner structure of the foam can also be better controlled. If necessary, the fibrous web can already be equipped with a first component farther away from the belt press and then with a second component shortly before the press if it is the second component, for example a catalyst, that starts the foam reaction.
It is beneficial to select a glass fibrous web with a binding agent percentage in the area of 0.1% to 20%, particularly from 0.1% to 7%. The lower the binding agent percentage is, the better the foaming components can enter and penetrate into the glass fibrous web. Usually, the binding agent is then only located on the crossing points between the glass fibers. The spaces between the glass fibers on the other hand are free for absorption of the foaming components. In addition, this has the advantage that the foam can build so that the pores formed during this process mainly settle in the spaces between the glass fibers. The small xe2x80x9cgas bubblesxe2x80x9d or voids are not destroyed right away through the glass fibers. With this, relatively thick multi-layer materials can be realized. Additionally, a low binding agent percentage has the advantage that the glass fibrous web can be handled more easily. In particular it can be unwound from a roll.
It is advantageous to select a glass fibrous web with a thermoplastic binding agent whose glass temperature is below a reaction temperature for foam building. At the glass temperature, the binding agent loses its binding characteristics, or xe2x80x9cadhesive power,xe2x80x9d at least partially. During the foaming process, this leads to a partial disintegration of the compound-formed fabric and to a xe2x80x9cmixingxe2x80x9d of the inner area of the foam matrix with fiber material. This improves the possibility of foaming because the bubbles created can push away the glass fibers, which are no longer bonded or no longer completely bonded, without being damaged. This way, the fibers become movable during the foaming process so that the risk of damage during a subsequent molding process and the xe2x80x9cdegradationxe2x80x9d of the reinforcement in bending and edge areas are reduced. The strength and stability of the material is improved. A reinforced foam matrix will result, which has improved acoustic insulation and an improved passive safety without expecting any loss of stability or other characteristics. In particular, no sharp edges are created when a head airbag is released.
The task is resolved with a multi-layer material of the kind described above in which the fiber reinforcement is formed by a fibrous web, which exists in the foam in a partially disintegrated form.
As explained above in connection with the manufacturing method, such a multi-layer material excels through the fact that, on the one hand, it is equipped with a fiber-reinforced foam, which displays good sound-dampening behavior and great strength, but that on the other hand it still has good forming and handling properties. In particular, the partial disintegration of the fibrous web enables good forming behavior.
Preferably, the fibrous web has a binding agent percentage in the area of 0.1 to 20%, particularly from 0.1% to 7%. The lower the binding agent percentage is, the better the foam can penetrate into the fibrous web.
It is particularly preferred if the binding agent is a thermoplastic binding agent with a glass temperature that is below a reaction temperature at the foaming process. Upon manufacture of the web and during transport, the binding agent holds together the fibers of the fibrous web as long as is required. However, if the foam encloses the fibers of the web, cohesion is no longer required or not to this extent. The binding agent can then soften and reduce or lose its adhesive power so that after the foaming process the fibers take on a position that is optimal for the foam.
Preferably, the top layer has the design of a bonding sheet, onto which an additional sheet material is glued. This way, a very compact and cohesive multi-layer material is obtained, which can be used directly for the production of interior limngs.